Solar cells are known in the art. A solar cell may include, for example, a photoelectric transfer film made up of one or more layers located between a pair of substrate. These layers may be supported by a glass substrate. Example solar cells are disclosed in U.S. Pat. Nos. 4,510,344, 4,806,436, 6,506,622, 5,977,477, and JP 07-122764, the disclosures of which are hereby incorporated herein by reference.
Substrate(s), sometimes called superstrate(s), in a solar cell are sometimes made of glass. Glass that is fairly clear in color and highly transmissive to visible light is sometimes desirable. Glass raw materials (e.g., silica sand, soda ash, dolomite, and/or limestone) typically include certain impurities such as iron, which is a colorant. The total amount of iron present is expressed herein in terms of Fe2O3 in accordance with standard practice. However, typically, not all iron is in the from of Fe2O3. Instead, iron is usually present in both the ferrous state (Fe2+; expressed herein as FeO, even though all ferrous state iron in the glass may not be in the form of FeO) and the ferric state (Fe3+). Iron in the ferrous state (Fe2+; FeO) is a blue-green colorant, while iron in the ferric state (Fe3+) is a yellow-green colorant. The blue-green colorant of ferrous iron (Fe2+; FeO) is of particular concern when seeking to achieve a fairly clear or neutral colored glass, since as a strong colorant it introduces significant color into the glass. While iron in the ferric state (Fe3+) is also a colorant, it is of less concern when seeking to achieve a glass fairly clear in color since iron in the ferric state tends to be weaker as a colorant than its ferrous state counterpart.
It has been found that the use of a low-iron highly transparent (optionally patterned) glass is advantageous for solar cell applications. The use of the low-iron composition in combination with the patterned surface(s) of the glass substrate(s) has been found to be advantageous with respect to optical properties, thereby leading to increased solar efficiency of a solar cell.
In certain example embodiments of this invention, a solar cell glass substrate has a visible transmission of at least 75% (more preferably at least 80%, even more preferably at least 85%, and most preferably at least about 90%). In making such a glass, a batch therefor includes a base glass (e.g., soda lime silica glass) and in addition comprises (or consists essentially of in certain other embodiments) a very small amount of total iron.
In the past some have tried to use cerium oxide in glass for solar cell applications as an oxidizer. However, it has been found that the use of significantly amounts of cerium oxide in solar cell glass can result in a loss of solar transmission after ultraviolet (UV) exposure, which is of course undesirable. Thus, in certain example embodiments of this invention, the use of cerium oxide is substantially avoided.
In this respect, it has surprisingly been found that the use of antimony (e.g., in the form of an oxide of antimony (Sb)) in high transmission low-iron glass for solar cells or the like results in a glass that need not suffer from the aforesaid problem associated with cerium oxide. Accordingly in certain example embodiments of this invention, antimony (Sb) is provided in low-iron high transmission glass. Thus, the resulting glass may include antimony (Sb) and be substantially free of cerium oxide so as to realize good stability of solar performance (e.g., no or reduced loss of total solar transmission after UV or sunlight exposure).
In certain example embodiments, the patterned glass substrate may have fairly clear color that may be slightly yellowish (a positive b* value is indicative of yellowish color). For example, in certain example embodiments, the patterned glass substrate may be characterized by a visible transmission of at least 90%, a total solar/energy value of at least 90%, a transmissive a* color value of from −1.0 to +1.0 (more preferably from −0.5 to +0.5, and most preferably from −0.2 to 0), and a transmissive b* color value of from 0 to +1.5 (more preferably from +0.1 to +1.0, and most preferably from +0.2 to +0.7). These properties may be realized at an example non-limiting reference glass thickness of from about 3-4 mm.
In certain example embodiments of this invention, in combination with the use of antimony (Sb), the glass has no more than 0.07% cerium oxide, more preferably no more than 0.06%, even more preferably no more than 0.04% cerium oxide, even more preferably no more than 0.02% cerium oxide, and possibly 0 or 0.01% cerium oxide.
In certain example embodiments of this invention, there is provided a solar cell comprising: a patterned glass substrate, wherein at least one surface of the patterned glass substrate has a surface roughness of from about 0.1 to 1.5 μm; first and second conductive layers with at least a photoelectric film provided therebetween; wherein the glass substrate is of a composition comprising:
Ingredientwt. %SiO267-75%Na2O10-20%CaO5-15%total iron (expressed as Fe2O3)0.001 to 0.06%cerium oxide0 to 0.07%antimony oxide0.01 to 1.0%wherein the glass substrate has visible transmission of at least 90%, a transmissive a* color value of −1.0 to +1.0 and a transmissive b* color value of from 0 to +1.5.
In other example embodiments of this invention, there is provided solar cell comprising: a glass substrate; a photoelectric film supported by at least the glass substrate; wherein the glass substrate is of a composition comprising:
Ingredientwt. %total iron (expressed as Fe2O3)0.01 to 0.06%antimony oxide 0.01 to 0.5%wherein the glass substrate has visible transmission of at least 90%, a transmissive a* color value of −1.0 to +1.0 and a positive transmissive b* color value.
In other example embodiments of this invention, there is provided a glass substrate comprising:
Ingredientwt. %SiO267-75%Na2O10-20%CaO5-15%total iron (expressed as Fe2O3)0.001 to 0.06%cerium oxide0 to 0.07%antimony oxide0.01 to 1.0%wherein the glass substrate has visible transmission of at least 90%, a transmissive a* color value of −1.0 to +1.0 and a transmissive b* color value of from 0 to +1.5.
In still further example embodiments of this invention, there is provided a method of making patterned glass, the method comprising: providing a molten glass batch in a furnace or melter comprising from 67-75% SiO2, from about 0.01 to 0.06% total iron, and antimony oxide; forwarding a glass ribbon from the furnace or melter to a nip between first and second rollers, at least one of the rollers having patter defined in a surface thereof, wherein the glass ribbon reaches the nip at a temperature of from about 1,900 to 2,400 degrees F.; at the nip, transferring the pattern from the roller(s) to the glass ribbon; the glass ribbon being at a temperature of from about 1,100 to 1,600 degrees F. upon exiting the nip; annealing the glass ribbon at least after the ribbon exits the nip, thereby providing a patterned glass having a visible transmission of at least 90%, from about 0.01 to 0.06% total iron, and from about 0.01 to 1.0% antimony oxide.